localized states

Abstract. We study the two-dimensional, disordered, attractive Hubbard model by the projector quantum Monte Carlo method and Bogoliubov-de Gennes mean-eld theory. Our results for the ground state show the appearance of a new phase with charge localization in the metallic regime of the non-interacting model. Contrary to the common lore, we demonstrate that mean-eld theory fails to predict this phase and is unable to describe the correct physical picture in this regime. PACS. 74.20.-z Theories and models of superconducting state { 74.25.-q General properties; correlations between physical properties in normal and superconducting states { 74.40.+k Fluctuations (noise, chaos, nonequilibrium superconductivity, localization, etc.) The transition from superconductor to insulator (SIT) in the presence of disorder continues to actively attract the interest of experimentalists and theoreticians, alike. Ex-perimentally, this transition has been observed in thin-lms of various materials by several dierent groups, re-viewed for example in [1]. Theoretically, attempts were made to model the original fermionic problem by an ef